Older people (age ≥65) living in cities with major marathons who were hospitalized for myocardial infarction or cardiac arrest on race days were about 13% more likely to die within the next 30 days than those hospitalized for events occurring on non-marathon days, according to Anupam Jena, MD, PhD, of Harvard Medical School, and colleagues.

But this delay probably wasn't the main driver of the marathon-related mortality increase identified in the study, Jena told MedPage Today. Rather, delays among those seeking treatment who were not transported to hospitals in ambulances may largely explain the findings.

Nearly a quarter (23%) of MI or cardiac arrest patients in the study did not arrive at hospitals by ambulance. Although the researchers were not able to determine the delay times for these patients, Jena said it is likely that delays were longer than those experienced by ambulance-transported patients.

"The mortality increases that we observed may very well be coming from those (self-transported) individuals who undoubtedly experienced longer transport times on the day of a marathon than they normally would," he said.

The message to the public, he added, is that "if you experience chest pain, shortness of breath, stroke-like symptoms, or any symptoms that require acute medical care on the day of a marathon, call 911. They should call 911 anyway, but it may be especially important on the day of a marathon."

Jena and colleagues analyzed Medicare data on hospitalizations for MI or cardiac arrest among Medicare beneficiaries in 11 U.S. cities hosting major marathons from 2002 through 2012.

They compared 30-day mortality among recipients hospitalized on the date of a marathon, those hospitalized on the same day of the week as the marathon in the five weeks before and after the race, and those hospitalized on the same day as the marathon but in surrounding ZIP code areas unaffected by the race.

Data from a national registry of ambulance transports were also analyzed to determine if transports occurring before noon on marathon days (when road closures were likely) were associated with longer scene-to-hospital transport times.

The analysis included 1,145 hospitalizations for MI or cardiac arrest at marathon-affected hospitals on marathon days and 11,074 hospitalizations on non-marathon days.

Hospitalization frequencies were similar on marathon and non-marathon days and the characteristics of the Medicare beneficiaries hospitalized on marathon and non-marathon dates were also similar.

This pattern persisted after adjustment for having five or more chronic medical conditions, a group that is unlikely to be hospitalized because of marathon participation.

No significant differences in mortality outcomes were found with respect to where patients were hospitalized or the treatments they received in the hospital.

No delays were found for evening transport or in areas unaffected by marathons.

"Taken together, our findings suggest that road closures, diversion of ambulance resources, and ensuing delays in hospital care may explain the higher mortality that we observed among patients with acute myocardial infarction or cardiac arrest who were hospitalized on dates of major marathons," the researchers wrote.

The difference in mortality observed in the study was substantial, with an estimated additional 3 to 4 deaths associated with hospitalization occurring on marathon day for every 100 events, Jena said.

"Emergency personnel and city officials need to be aware of this, and they need to make sure there are plans in place to address it," he added.